We, humans, have explored the vast oceans and deep reaches of space, but there is one frontier much closer to home which we know even less about, and it’s right below your feet. From where you’re standing right now the centre of the earth is over 6,000 km down. Trillion tons of rock trapped by gravitational forces and formed over millions of years. Where there was once forests there are now only carbon fossils under kilometres of dirt.

What you’re standing on right now forms part of the earth’s crust. This layer of earth that we built our civilization on, which we all depend on to live and contains all that we fear, forms only 1% of the total volume of this planet. The rest is a combination of molten and solid rock that we can never see, but still plays a huge role on the planet. Besides shaping continents, forming mountains and valleys, and holding the oceans, the movements made under the earth drive earthquakes, tsunamis and volcanic eruptions.

These natural dangers aren’t visible to the eye. You cannot predict when exactly a volcano will cause havoc, for there are volcanoes that have been spewing lava for millennia but haven’t caused much damage for centuries, and there are dormant volcanoes that can erupt violently without much warning and wipe out everything in its path. Earthquakes can topple skyscrapers, break roads and curve railroad tracks. Undersea earthquakes can and have caused tremendous amounts of damage in the form of tsunamis that span across the globe. Megatsunamis happen when a rockslide, often caused by an earthquake, displaces a large amount of water, forming waves between 100 and 170 meters tall.

With so much destruction that can happen, it’s no wonder that scientists are at work trying to figure out exactly what’s going on down there. By using a combination of thousands of sensors and scanners, humanity is now capable of taking virtual X-rays of the earth, giving us access to information that can save many lives in the future.

On Wednesdays at 9 PM on National Geographic (ch 220, from May 27^th)